The present invention relates to an optical head and an optical memory device for recording and reproducing information utilizing a light beam.
FIG. 18 shows the structure of a magneto-optical recording and reproducing head as an example of an optical head of a conventional optical memory device.
As shown in the drawing, a light beam irradiated from a light source 1801 is passed through a lens 1802, beam splitters 1803 and 1804, and is condensed on a magneto-optical recording medium by an objective lens 1805 and reflected from a surface of the magneto-optical medium 1806 as a light beam including information. A part of the reflected light beam is divided by the beam splitter 1804 and directed to an optical system comprised of a lens 1807, a Wollaston prism 1808, and a photodiode 1809. Thereby, a magneto-optical reproducing signal is obtained.
The other part of the reflected light beam divided by the beam splitter 1803 is directed to an optical system comprised of a lens 1810, a beam splitter 1811, a knife-edge 1812, a photodiode 1813 to obtain therefrom a focusing error signal. The reflected light beam is divided by the beam splitter 1811 and radiated on a photodiode 1814 to thus obtain a tracking error signal.
However, a conventional optical head has many optical members constituting the overall optical system for detecting signals, which has a problem due to its large size and high cost.
Accordingly, an object of the present invention is to provide an optical head of small size and low production cost. Another object of the invention is to provide an optical memory device employing such an optical head.